The goal of this proposal is to establish the feasibility of human liver slice cultures for the study of xenobiotic metabolism. This new in vitro system has been extensively tested in our laboratory and others with tissue slices from other species and using other end points then xenobiotic metabolism. The novel aspect of this proposal is the application of this prior experience to human tissue and the thorough optimization of all connected parameters such that a powerful new tool, which will find its place in mechanistic human hepatotoxicity studies is made available to the scientific community. Since human tissues are not conveniently available at any time it is important to investigate storage modalities such as banking of cryopreserved slices under liquid nitrogen and cold preservation in special tissue preservation solutions at just above 0 degrees C. Our limited amount of preliminary information seems to indicate that cryopreservation and cold preservation of human tissue slices can be optimized such that metabolic activities of fresh tissue are retained. Through systematic evaluation of the relevant parameters in cryo and cold preservation such as optimal composition of solutions, freezing rate, cryoprotectants vitrification conditions, rewarming rates and their effect on the maintenance of xenobiotic metabolism by the human tissue much needed general knowledge on this new in vitro tool in biochemical pharmacology will emerge. The stability of xenobiotic metabolic pathways during culture of human liver and kidney slices at quasi physiological conditions will teach what can maximally be expected from this in vitro system. Since the focus of this proposal is integrated xenobiotic metabolism i.e. the tight coupling of phase I and II under the conditions of intermediary metabolic control of an intact cellular system we will not attempt at this time to determine amounts, maximal activities, rates of synthesis and degradation of individual enzymes, but will focus on complex metabolite patterns of a few standard xenobiotics and their shifting appearance as individual enzymes drop out or emerge during culture.